110 Prof. E. Edlund's Investigation of the Electric Light. 



Daring the experiments the apparatus was placed in the lamp 

 belonging to it. The length of the luminous arc was not di- 

 rectly determined by measuring the distance between the points, 

 but, by means of a lens introduced into the lamp, a magnified 

 image was taken, which was projected on a scale on the opposite 

 wall of the room. The distance between the parallel divisions 

 of the scale was 10 millims. The glass lens magnified twenty- 

 five times. Each division of the scale corresponded to about 0*4 

 millim. To make the image of the luminous arc very distinct, 

 most of the daylight was excluded from the working-room. 



First set of Experiments. 



4. The battery consisted of seventy-six elements, the pole- 

 points were of hard carbon, externally of the same kind as that 

 of the battery. When only 0'6 inch of the rheostat was in- 

 serted in the circuit and the carbon points were in contact, the de- 

 flection of the tangent-compass amounted to 63° 30'; and when 

 8*4 inches were inserted, 51° 5'. We obtain from this 11*994 

 units of resistance as the resistance M outside of the rheostat. 

 After the termination of the experiment the tangent-compass 

 showed 64° in the first, and 52° 10' in the latter case. From 

 this we obtain M = 12577; and the mean value for M during 

 the experiments was 12*285 units of resistance. 



Experiment I. When an electric light of the length of 5 

 divisions of the scale was formed, and 06 inch of the rheostat 

 interposed in the circuit, the intensity of the current was = 

 Tg. 51° 5'. When the carbon points were thereupon brought in 

 contact and pressed hard against each other, 8*4 inches of the 

 rheostat had to be introduced into the circuit in order to bring 

 the tangent-compass to the angle of deflection mentioned. Thus 

 the total resistance in this voltaic arc was 8*4— 0'6 = 7*8 units. 

 With the same intensity the following results were obtained for 

 shorter arcs : — 



Length of the arc = 4 parts of the scale. Resistance = 7'6 



33 33 " } i i) a »'u 



33 33 " 3i 33 33 '*•*■ 



33 33 -*■ 33 33 33 u ** 



We thus obtain a-t-56 5 =7'8, a + 4b 4 ~7'6, a + Sb 8 = 7'S, 

 a + 2b 2 = 7'l, and a + b l = 6-9. For each increase of one division 

 of the scale in the length of the arc, the resistance is increased 

 by 0*2 unit. We may thus conclude that b b — b 4 = b B — bc l = b lJ 

 and « = 6'7. 



minous arc by altering the position of the points, while I read off the inten- 

 sity on the galvanometer. I avail myself of this opportunity of heartily 

 thanking Professor Stenberg. 



